【作者】 蒋鸣；

【导师】 刘常升； 李国喜；

【作者基本信息】 东北大学 ， 材料学， 2008， 博士

【摘要】 随着我国各主要油、气田已逐渐进入了开采的中后期阶段,开采出的石油、天然气中,水、二氧化碳及硫化氢等腐蚀介质的含量都逐渐增加,使得石油管的腐蚀程度日益严重。而目前应用较多的防腐技术存在成本较高或耐蚀性较差等缺点,因此,寻求新的防腐技术仍然迫在眉睫。由于热浸镀铝及铝锌合金镀层具有良好的耐蚀性且成本较低,因此本文系统研究了热浸镀铝及铝锌合金对石油管常用材质非调质N80钢防腐性能、力学性能的影响及机理,并就如何进一步改善热浸镀后N80钢的防腐、力学性能进行了研究和探讨。首先详细研究了一浴法、二浴法及钝化法三种热浸镀铝工艺对镀层质量和性能的影响,从镀层厚度、连续性、耐蚀性和显微组织形貌几个方面进行分析比较。通过对三种工艺的研究来确定非调质N80钢热浸镀铝的工艺方法。三种工艺方法得到的镀铝层均由表面纯铝层和中间合金层组成,但在相同的参数下,镀层的厚度、致密性及耐蚀性不同。对于镀层总厚度,钝化法的最厚,二浴法的次之,一浴法的最薄；而对于镀层致密性及耐蚀性,二浴法的最佳,一浴法的次之,钝化法的最差。与其他两种工艺方法相比,二浴法工艺稳定,得到的镀铝层质量更好,因此本文确定非调质N80钢的热浸镀铝工艺为二浴法。研究了激光重熔工艺参数对扩散型热浸镀铝层裂纹和空洞的影响,采用JHM-1GY-400型YAG(晶体)激光器对扩散型热浸镀铝Q235钢的表面进行激光重熔处理,优选出最佳工艺参数,借助于扫描电镜、电子探针、金相显微镜、X射线衍射仪、显微硬度计等设备对激光处理后镀铝层的显微形貌、组织结构及性能进行了分析。通过测定在3.5%NaCl水溶液中阳极极化曲线,讨论了激光重熔处理对镀铝层耐蚀性的影响。适当的激光重熔处理可消除镀铝层中的裂纹及空洞,镀层变得更加致密,从而使其在3.5%NaCl水溶液中的耐蚀性高于未激光处理的镀层。并且其显微组织发生了高铝ξ相(FeAl2)向低铝β2相(FeAl)的转变,导致镀层显微硬度和脆性降低,镀层综合性能得到改善。通过比较镀铝前后非调质N80钢的显微组织和力学性能,研究了热浸镀铝过程对其力学性能的影响。为了提高镀铝后N80钢的力学性能,采用正交实验法对镀铝后的N80钢进行调质和亚温淬火处理。热浸镀铝后N80钢组织中V、Ti等合金元素的析出相长大、珠光体部分球化,使其强度、塑性有所下降,其中抗拉强度下降了13%,不能满足API SPEC 5CT标准的要求。通过适当的调质处理或亚温淬火、回火处理,可使镀铝后N80钢的抗拉强度由663MPa提高至810～845MPa,塑性和冲击韧性等力学性能也有所改善,但增加了生产成本且镀铝层会发生扩散反应而使镀层耐蚀性有所下降。通过试验研究,本文提出采用高温热浸镀铝→水淬→高温回火的方法来对非调质N80钢进行处理,此方法在获得质量良好的镀铝层的同时,得到了与亚温淬火、回火处理后相同的力学性能,且工艺简单,成本较低。采用静态浸泡试验和电化学试验研究了热浸镀铝对非调质N80钢防腐性能的影响,并且,为了进一步提高热浸镀铝层的耐蚀及耐结垢性能,在热浸镀铝层上分别化学镀Ni-P合金和涂敷纳米环氧涂层,研究两种复合镀层的耐蚀及耐结垢性能。热浸镀铝层因其表面生成了一层致密的Al2O3保护膜而使N80钢的防腐性能显著提高。而化学镀镍层和环氧树脂涂层因具有表面光滑、与铝镀层结合力强,可使铝镀层与环境隔离等特点,而使热浸镀铝加化学镀Ni-P合金复合镀层和热浸镀铝加环氧树脂复合涂层均可以进一步提高N80钢的耐蚀及耐结垢性能。其中热浸镀铝加环氧树脂复合涂层施工方便,成本较低,具有广阔的应用前景。通过对非调质N80钢热浸镀55%Al-Zn合金的水溶液助镀法和电解活化助镀法的研究和比较,提出了一种新的助镀方法,即电解活化加浸4%K2ZrF6水溶液助镀法。此方法可克服水溶液助镀法和电解活化助镀法各自的不足而得到质量良好的镀层。在此基础上,通过静态浸泡试验、电化学试验研究了热浸镀55%Al-Zn合金后N80钢在不同腐蚀介质中的耐蚀性；通过拉伸和冲击试验研究了热浸镀Al-Zn合金过程对N80钢力学性能的影响。非调质N80钢热浸镀55%Al-Zn后,在3%NaCl水溶液及人工配制的腐蚀介质中的耐蚀性均显著提高,接近于热浸镀铝后的耐蚀性。同时,热浸镀过程使N80钢基体的组织变得更加均匀细小,析出相数量增加且尺寸无明显变化,从而导致N80钢的强度、塑性及冲击韧性等力学性能显著提高,并且其工艺简单,生产成本较低,通用性强,说明采用此技术来提高石油管的防腐性能是可行的。更多还原

【Abstract】 In our country, the most of oil and gas mining have come into the middle and later stage. In many oil and gas fields, highly water, carbon dioxide, hydrogen sulfide and element sulfur have been found. The corrosion problems of petroleum pipe become more and more harsh. At the present time, the preservation technologies of petroleum pipe have many disadvantages, such as highly cost and lowly corrosion resistance. So, research of new preservation technologies of petroleum pipe is very important.Because hot dipped Al and Al-Zn alloy coating have excellent corrosion resistance and lowly cost, the effect of hot dipped Al and Al-Zn alloy coating on properties of non-quenched and tempered N80 steel was studied systematically. And the improvement of properties of hot dipped coated N80 steel also was studied.Firstly, the effects of one bath flux method, two bath flux method and passivating method on quantities and properties of hot dipped aluminum coatings were studied. Meanwhile, the thickness, continuity, corrosion resistance and microstructure of hot dipped aluminum coatings were analyzed and compared. The optimal technology of petroleum pipe was determined by comparing coating quality. The results indicated that the microstructure of hot dipped coatings by 3-kind methods have the same structure, which were composed of aluminum overlay and intermetallic compound layer. But, under the same parameters, the thickness, continuity and corrosion resistance of coatings were different. In terms of thickness, the coating by passivating method was the biggest, the coating by two bath flux method was the second place and coating by one bath flux method was the smallest; In terms of continuity and corrosion resistance, the coating by two bath flux method was the best, coating by one bath flux method was the second place and coating by passivating method was the worst. So, the optimal hot dipped Al technology of petroleum pipe was two bath flux method.The effects of laser technical parameters on cracks and defects of hot dipped Al coating were studied. The optimal laser technical parameters were determined. And the microstructure and properties of laser remelted coating also were studied by means of SEM, EPMA, X-ray diffraction and micro-hardness measure. The results showed that the laser remelted coating treated by reasonable parameters has a compact microscopic structure, it was free from cracks and defects. The phase in the coating was changed from Al-rich phase to Al-poor phase. By laser treating, corrosion resistance of hot dipped Al coating could be improved, and microhardness and brittleness could be reduced.The effects of hot dipped Al process on mechanical properties of non-quenched and tempered N80 steel were studied, and the improvement of mechanical properties of hot dipped Al coated N80 steel was also studied through orthogonal method. The results showed that the strength and plasticity of the N80 steel were reduced by hot dipped Al process, which could not meet requirements of API SPEC 5CT seven edition. The decrease of mechanical properties was due to coarsening of precipitated phase and spheroidization of pearlite. And the ultimate tensile of aluminum coated steel could be rised from 663 MPa to 810～845 MPa by reasonable quenching and tempering or subcritical quenching and tempering treatment, the plasticity and impact toughness could also be improved. But the cost could be increased and coating quality could be reduced. Base on the above experiments, a new hot dipped Al process contained of hot dipped Al in high temperature, water quenching and tempering was put forward. The mechanical properties and coating quality could be greatly improved by the new process, which was of low cost and simple technology.The effects of hot dipped Al coating on corrosion resistance of non-quenched and tempered N80 steel were studied by using of static coupon testing and electrochemical testing, and the further improvement of corrosion and scaling resistance of hot dipped coated N80 steel were also studied. The results showed that hot dipped Al coating could improve the corrosion resistance of non-quenched and tempered N80 steel obviously, which was attributed to the formation of stable Al2O3 covering layer. The corrosion and scaling resistance of N80 steel could be further improved through electroless Ni-P plating or painting epoxy resin on Al coating because the two coatings have smooth surface, good adhesion and high barrier property. And composite coating contained hot dipped Al coating and epoxy resin layer appeared wide application prospect.Hot dipped 55%Al-Zn fluxes for non-quenched and tempered N80 steel were studied. In comparison with other flux methods, authors found out a kind of new flux method that has two steps:electrolytic active flux and 4% K2ZrF6 flux. And better properties of the coatings were obtained with the new flux method. On this base, the application feasibility of hot dip55%Al-Zn technology in petroleum pipe corrosion protection was studied. The results showed that hot dipped55%Al-Zn coating could improve the corrosion resistance of non-quenched and tempered N80 steel obviously. After hot dipped55%Al-Zn alloy, the strength and plasticity of the alloy-coated steels could also be greatly improved. So, using 55%Al-Zn alloy coating to protect petroleum pipe is feasible.更多还原